You have earned that leave the same as you have earned the dollars DFAS deposits in your checking account. Selling your leave back to the military is a bad deal and you shouldn't ever feel obligated to do that instead of taking it as leave in order to "help out" the military. Moreover, your opportunity to take that leave has thus far been limited by deployment. It is not your fault that you have a high leave balance - it's to your credit that you've worked so much with so little time off over the last few years.
So - work in good faith with your DH to schedule that leave so that the clinic is minimally disrupted. If the DH won't permit you to use it all before separating, have your reasonable and willing CO bottom line it and to hell with the DH.